Wireless monitoring or security systems include one or more sensor/transmitter units which send signals, e.g., coded radio-frequency (RF) message packets, to a system controller. The system controller decodes the message packets and, based on the content of the packets, may produce an alarm or other indication of a condition at the sending sensor/transmitter unit. The sensor condition may indicate the existence of a fire, an intrusion, an emergency, the failure of an appliance, or other condition desired to be monitored. Additionally, a sensor/transmitter may send periodic supervisory message packets.
The system controller includes one or more antennas for receiving the message packets. Every environment where a security system may be used (e.g., home, business, warehouse, etc.), includes other electronic signals, commonly known as "noise", that are received on the system controller antennas. Much of the noise is at a relatively low energy level and does not typically disrupt the reception of sensor/transmitter signals. Therefore, the low-level noise can be ignored by the security system.
When the noise reaches a certain level, however, it may prevent or disrupt the reception of the sensor/transmitter signals by the system controller. The disruption of the sensor/transmitter signals is typically referred to as "jamming." The jamming may be intentional, i.e., to defeat the security system, which an intruder may abruptly or gradually introduce into the security system environment. The jamming may also be unintentional, i.e., from a source generating a signal or by-product signal of sufficient strength to disrupt the reception of sensor/transmitter signals.
In either case, the jamming signals may prevent or disrupt the reception of sensor/transmitter signals by the system controller. Consequently, the system controller may not receive alarm message packets or supervisory message packets from one or more sensor/transmitters. The failure to receive the sensor/transmitter signals greatly compromises the effectiveness of the security system. Indeed, the Underwriters Laboratory (UL) requires an audible and visual indication at the system controller if there is any unwanted (interfering) transmission for a continuous period of 20 seconds or more, that would inhibit any status change signaling within the system (i.e., where the interfering transmission would prevent the detection of transmissions from the transmitters within the security system).
A disruption in reception may also be caused by insufficient transmission strength due, for example, to a low battery condition in one of the sensor/transmitters, though perhaps not so low so as to cause an indication of such. The incorrect interpretation of such conditions as a jamming condition (i.e., an alarm condition) may cause a homeowner unnecessary stress and perhaps false-alarm fees from a monitoring company.